1. Field of the Invention
The present invention relates to an Al—Ni—La—Cu alloy sputtering target comprising Ni, La and Cu, and a manufacturing method thereof. Specifically, the invention relates to an Al—Ni—La—Cu alloy sputtering target capable of decreasing initial splashing generated in an initial stage of sputtering upon depositing a thin film by using a sputtering target, and a manufacturing method thereof.
2. Description of the Related Art
Al-based alloys have been generally used with a reason of their low electrical resistivity and easy processability in the fields of flat panel displays (FPD) such as liquid crystal displays (LCD), plasma display panels (PDP), electroluminescence displays (ELD), field emission displays (FED) and micro electro mechanical system (MEMS) displays, touch panels, electronic paper and the like, and have been utilized as materials for interconnection films, electrode films, reflection electrode films and the like.
For example, an active matrix type liquid crystal display has a thin film transistor (TFT) as a switching device, a pixel electrode comprising a conductive oxide film, and a TFT substrate having interconnections including scanning lines and signal lines. For interconnection materials constituting the scanning lines and the signal lines, thin films of pure Al or Al—Nd alloy have generally been used. However, in a case where various kinds of electrodes formed by such thin films are in direct contact with pixel electrodes, since insulating aluminum oxides or the like are formed at their interface to increase electrical contact resistance, a barrier metal layer comprising a metal having a high melting point such as Mo, Cr, Ti or W is interposed between the interconnection material of Al and the pixel electrode for decreasing the electrical contact resistance.
However, the method of interposing the barrier metal layer as described above involves a problem of complicating manufacturing steps to increase the production cost.
Then, for providing a technique capable of direct contact between a conductive oxide film constituting a pixel electrode and a interconnection material not by way of a barrier metal layer (direct contact technique), a method of using a thin film of Al—Ni alloys, or Al—Ni alloys that further contain a rare earth element such as Nd or Y has been proposed (JP-A-2004-214606). By using the Al—Ni alloy, since Ni-containing conductive precipitates or the like are formed at the interface to suppress the formation of insulating aluminum oxides or the like, the electrical contact resistance can be kept lower. Further, in a case of using the Al—Ni-rare earth element alloys, heat resistance is further enhanced.
By the way, for forming an Al-based alloy film, a sputtering method of using a sputtering target has been adopted generally. The sputtering method is a method of forming plasma discharge between a substrate and a sputtering target made of a material identical with the thin film material, colliding a gas ionized by the plasma discharge against the sputtering target thereby ejecting atoms of the sputtering target, and depositing them on the substrate to prepare a thin film. Different from a vacuum vapor deposition method, the sputtering method has an advantage capable of forming a thin film of a composition identical with that of a sputtering target. Particularly, since an alloy element such as Nd which is not dissolved in an equilibrium can dissolve in the Al-based alloy film formed by the sputtering method and the Al-based alloy film provides an excellent performance as a thin film, this is an industrially effective method of preparing a thin film and development has been proceeded for the sputtering target as the material therefor.
In recent years, for coping with the increase of the productivity of FPD or the like, the deposition rate during sputtering step has tended to be increased than usual. For increasing the deposition rate, it is most convenient to increase a sputtering power. However, when the sputtering power is increased, since sputtering failure such as splashing (fine molten particles) is generated to result in defects in interconnection films or the like, this gives a drawback such as lowering of the yield and operation performance of FPD.
Then, with an aim of preventing the generation of the splashing, methods described, for example, in JP-A-10-147860, JP-A0-10-199830, JP-A-11-293454 and JP-A-2001-279433 have been proposed. Among them, each of JP-A-10-147860, JP-A-10-199830, and JP-A-11-293454 is based on the view that the splashing is caused by fine voids in the structure of a sputtering target and intends to prevent the generation of the splashing by controlling a dispersion state of compound particles of Al and rare earth element in an Al matrix (JP-A-10-147860), controlling the dispersion state of a compound of Al and a transition element in the Al matrix (JP-A-10-199830), or controlling the dispersion state of an intermetallic compound of an additive element and Al in a sputtering target (JP-A-11-293454). Further, JP-A-2001-279433 discloses a method of suppressing the generation of surface defects accompanying machining by controlling the hardness of a sputtered surface and then performing finishing machining for decreasing arcing (abnormal discharge) that causes the splashing.
On the other hand, a technique of preventing warp of a sputtering target caused by heating during manufacture of a large-scaled sputtering target has been disclosed (JP-A-2006-225687). JP-A-2006-225687 is directed to an Al—Ni-rare earth element alloy sputtering target as an object and proposes a method capable of suppressing the deformation of the sputtering target by causing a compound having an aspect ratio of 2.5 or more and a circle equivalent diameter of 0.2 μm or more to be present with a given number or more along a cross section vertical to the plane of a sputtering target.